Using a balance type micro-indentor, capable of applying small forces to the intimal surface of an aortic segment by means of a small flat prodder tip and measuring the resulting indentation, surface hardness of tissue from healthy animals will be mapped and compared with similar results from animals with experimental atherosclerosis. Devices for studying the jet erosion strength of the endothelium and the puncture resistance of the intima and supporting structures will be built. Understanding of these tissue properties will throw light on the role of tissue factors in the pathogenesis of atherosclerosis.